Design of Transformer-Based Boost Converter for High Internal Resistance Energy Harvesting Sources With 21 mV Self-Startup Voltage and 74% Power Efficiency

Thin-film thermoelectric generators (TEG) or graphene-based microbial fuel cells (MFC) are emerging energy harvesting sources with promising power density and sustainability. Nevertheless, conventional transformer-based boost converters commonly used to achieve autonomous low voltage startup encounter low efficiency and potential startup problems with these novel power sources due to their high internal resistance. In this paper, an improved design of transformer-based boost converter addressing these issues is demonstrated with prototype chip fabricated using a standard 0.13 μm CMOS process. The self-start oscillation does not rely on the conventional LC resonant principle, but instead is dependent on the MOS transistor's active-over-leakage current ratio and the mutual coupling between the two identical transformer coils. Circuit design techniques to regulate output voltage and to track system's maximum power point (MPP) of this boost converter are presented. Measurement results confirmed that the proposed circuit works with either low threshold voltage or native MOS transistors. It needs minimum self-startup voltage of 21 mV (at 5.8 μW input power) and minimum startup power of 1.3 μW (at 35 mV input voltage) respectively. The maximum output power is 2 mW and peak power conversion efficiency is 74% at a regulated output voltage of 1 V.